The present invention relates generally to substrate cleaning and, more particularly, to a wafer cleaning module and a method for cleaning a surface of a substrate.
As is well known to those skilled in the art, wafer preparation and cleaning operations are performed in the fabrication of semiconductor devices. One of the functions of a wafer cleaning operation is to remove contaminants such as adhered particles and adsorbed compounds, e.g., chemicals, from the surface of the wafer. For example, during a chemical mechanical planarization (CMP) operation designed to achieve global and local planarization of a wafer surface, abrasive particles in the slurry may bond to the wafer surface and chemicals in the slurry may be adsorbed over the wafer surface.
As the feature size of integrated circuits continues to decrease, it is imperative that wafer surfaces being subjected to fabrication operations be as close to 100% free of contamination as is practical. In one known cleaning operation, wafers are scrubbed with brushes in one or more brush scrubbing stations to remove contaminants from the wafer surface. During brush scrubbing, local jets created by the mechanical movements of the brushes produce sufficient shear forces to dislodge a high percentage of contaminants from the wafer surface. In some instances, the brush scrubbing operation is supplemented by megasonic agitation, which shakes the wafer surface and thereby assists in the breaking of the intermolecular bonding between contaminants and the wafer surface. In other instances, chemicals such as KOH and NH4OH are introduced at the cleaning interface to enhance the cleaning process. When such chemicals are used, the distortion forces created by ions of the same electrical charge help overcome the intermolecular bonding between contaminants and the wafer surface.
The cleaning operations discussed above suffer from a number of shortcomings. First and foremost, these cleaning operations do not produce a contamination-free wafer because they do not remove about the last 1% of contaminants, which are bonded to the wafer surface with extremely strong intermolecular forces. Second, conventional brush scrubbing operations are coordinate centric. In other words, conventional brush stations do not scrub the center of wafers and the edges of wafers uniformly. Accordingly, multiple cleaning operations may be required to clean the entire surface of the wafer thoroughly. This is undesirable because it increases the overall time expended on wafer cleaning and thereby reduces throughput. Third, the brushes may cause micro-scratches on the wafer surface and thereby damage the wafer to such an extent that it must be discarded as scrap. This disadvantageously lowers the yield of the fabrication process. Fourth, the brushes may recontaminate the wafer surface by introducing residues of previously cleaned substrates to such a degree that multiple cleaning operations are required.
In view of the foregoing, there is a need for a method for cleaning a surface of a semiconductor wafer that provides contamination-free wafers without reducing throughput and without scratching or otherwise damaging the surface of the wafer.
Broadly speaking, the present invention fills these needs by providing methods for cleaning a surface of a substrate by agitating a liquid-crystal mixture of a saturated solution. The present invention also provides a wafer cleaning module.
In accordance with one aspect of the present invention, a first method for cleaning a surface of a substrate is provided. In this method, an amount of a solution is supplied on a surface of a substrate. Next, crystallization of the solution is initiated to form a liquid-crystal mixture. Once the liquid-crystal mixture is formed, relative motion between the liquid-crystal mixture and the substrate is created to dislodge contaminants adhered to the substrate. The method is particularly useful in the cleaning of semiconductor wafers.
In one embodiment, the operation of initiating crystallization of the solution includes heating the solution. By way of example, the solution may be heated with infrared radiation or may be heated by applying heated gas to the solution.
In one embodiment, the operation of creating relative motion between the liquid-crystal mixture and the substrate includes rotating the substrate. Alternatively, the relative motion may be created by agitating the liquid-crystal mixture with a brush.
In accordance with another aspect of the present invention, a second method for cleaning a surface of a substrate is provided. In this method, a solution is applied on a pad. Crystallization of the solution is then initiated to form a liquid-crystal mixture on the pad. Thereafter, the method continues by contacting a surface of the substrate with the pad. In one embodiment, the pad is selected from the group consisting of a belt-type pad, a rotary pad, and an orbital-type pad.
In accordance with yet another aspect of the present invention, a third method for cleaning a surface of a substrate is provided. In this method, a bath of solution is provided. Thereafter, a substrate is placed in the bath of solution. Crystallization of the solution is then initiated to form a liquid-crystal mixture. Once the liquid-crystal mixture is formed, relative motion between the liquid-crystal mixture and the substrate is created.
In one embodiment, the operation of initiating crystallization of the solution includes adjusting a temperature of the solution to a temperature at which crystallization occurs. In one embodiment, the operation of creating relative motion between the liquid-crystal mixture and the substrate includes either rotating the substrate or subjecting the liquid-crystal mixture to megasonic agitation.
In accordance with still another aspect of the present invention, a wafer cleaning module is provided. The wafer cleaning module includes a belt-type pad and a dispenser for dispensing a saturated solution. The wafer cleaning module further includes a carrier head for carrying a semiconductor wafer. Also included in the wafer cleaning module is a crystallization inducer for inducing crystallization of the saturated solution. The dispenser, the carrier head, and the crystallization inducer are disposed above the belt-type pad such that the crystallization inducer is situated between the dispenser and the carrier head. In one embodiment, the crystallization inducer is an infrared lamp.
The wafer cleaning module and the methods for cleaning surfaces of substrates of the present invention are advantageous as they have the capability of yielding a contamination-free substrate by removing the last 1% of contaminants adhered to substrate surfaces by extremely strong intermolecular bonding. More particularly, the crystal bath cleaning method of the present invention is beneficial because it has the ability to clean a substrate having a heterogeneous surface without introducing cross-contamination or micro-scratches onto the substrate surface. Additional advantages of the wafer cleaning module and the methods for cleaning surface of substrates of the present invention are that they are flexible, are not coordinate centric, and do not reduce throughput because they do not create a bottleneck in the overall cleaning process.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.